Flickering when selecting parameters on page "ESTIMATE"

With shinystan v2.6.0, I get a strange bug when selecting parameters on page "ESTIMATE". The input field "Select or enter parameter names" as well as the plot start flickering heavily, making further use of that input field impossible (and the plot almost impossible to read).

Reproducible steps:

1. Create file schools.stan with content (modified from https://github.com/stan-dev/rstan/wiki/RStan-Getting-Started):

   // saved as schools.stan
   data {
     int<lower=0> J;         // number of schools 
     real y[J];              // estimated treatment effects
     real<lower=0> sigma[J]; // standard error of effect estimates 
   }
   parameters {
     real mu;                // population treatment effect
     real<lower=0> tau;      // standard deviation in treatment effects
     vector[J] eta;          // unscaled deviation from mu by school
   }
   transformed parameters {
     vector[J] theta = mu + tau * eta;        // school treatment effects
   }
   model {
     target += student_t_lpdf(mu | 7, 0, 5);  // prior for mu
     target += student_t_lpdf(tau | 7, 0, 1);  // prior for tau
     target += normal_lpdf(eta | 0, 1);       // prior log-density
     target += normal_lpdf(y | theta, sigma); // log-likelihood
   }
   

2. Run

   library(rstan)
   options(mc.cores = parallel::detectCores())
   rstan_options(auto_write = TRUE)
   
   schools_dat <- list(J = 8, 
                       y = c(28,  8, -3,  7, -1,  1, 18, 12),
                       sigma = c(15, 10, 16, 11,  9, 11, 10, 18))
   
   fit <- stan(file = "schools.stan", data = schools_dat, seed = 2098606L)
   
   library(shinystan)
   launch_shinystan(fit)
   

3. In the shinystan app, switch to page "ESTIMATE".
4. Select parameter mu.
5. Now, I already get a mild version of the flickering described above.
6. Enter theta in the "Add parameters by regex search" input field and click on "Search".
7. Now, I get the heavy flickering described above. Interestingly, after switching the browser tab and switching back to shinystan, the flickering stops, but the "Select or enter parameter names" input field is still unusable. Only the regex input field works, but when using it, the flickering starts again.

Session info:

I observed this with two different browsers on Ubuntu 20.04.3 LTS: Firefox and Chromium. I also observed this on Windows 10, but there I only tested Firefox. For the R packages (reduced to the content I deemed more or less relevant; tell me if you need more):

> sessioninfo::session_info()
- Session info --------------------------------------------------------------------------------------------------------
 setting  value
 version  R version 4.1.3 (2022-03-10)
 [...]
 ui       RStudio
 [...]
 rstudio  1.4.1717 Juliet Rose (desktop)
 [...]

- Packages ------------------------------------------------------------------------------------------------------------
 ! package       * version    date (UTC) lib source
   [...]
   bayesplot       1.9.0      2022-03-10 [1] CRAN (R 4.1.3)
   [...]
   bslib           0.3.1      2021-10-06 [1] CRAN (R 4.1.1)
   [...]
   callr           3.7.0      2021-04-20 [1] CRAN (R 4.0.5)
   [...]
   fontawesome     0.2.2      2021-07-02 [1] CRAN (R 4.1.1)
   [...]
   ggplot2         3.3.5      2021-06-25 [1] CRAN (R 4.1.0)
   ggridges        0.5.3      2021-01-08 [1] CRAN (R 4.0.3)
   [...]
   htmltools       0.5.2      2021-08-25 [1] CRAN (R 4.1.1)
   htmlwidgets     1.5.4      2021-09-08 [1] CRAN (R 4.1.1)
   [...]
   jquerylib       0.1.4      2021-04-26 [1] CRAN (R 4.0.5)
   jsonlite        1.8.0      2022-02-22 [1] CRAN (R 4.1.2)
   [...]
   knitr           1.38       2022-03-25 [1] CRAN (R 4.1.3)
   [...]
   loo             2.5.1      2022-03-24 [1] CRAN (R 4.1.2)
   [...]
   markdown        1.1        2019-08-07 [1] CRAN (R 4.0.0)
   [...]
   rlang           1.0.2      2022-03-04 [1] CRAN (R 4.1.2)
   rmarkdown       2.13       2022-03-10 [1] CRAN (R 4.1.3)
   [...]
   rstan         * 2.26.6     2021-12-15 [1] local
   rstudioapi      0.13       2020-11-12 [1] CRAN (R 4.0.3)
   sass            0.4.1      2022-03-23 [1] CRAN (R 4.1.2)
   scales          1.1.1      2020-05-11 [1] CRAN (R 4.0.0)
   sessioninfo     1.2.2      2021-12-06 [1] CRAN (R 4.1.2)
   [...]
   shiny         * 1.7.1      2021-10-02 [1] CRAN (R 4.1.1)
   shinyjs         2.1.0      2021-12-23 [1] CRAN (R 4.1.2)
   shinystan     * 2.6.0      2022-03-03 [1] CRAN (R 4.1.2)
   shinythemes     1.2.0      2021-01-25 [1] CRAN (R 4.0.3)
   [...]
   StanHeaders   * 2.26.6     2021-12-15 [1] local
   [...]
   V8              4.1.0      2022-02-06 [1] CRAN (R 4.1.2)
   [...]
   withr           2.5.0      2022-03-03 [1] CRAN (R 4.1.2)
   [...]
   xtable          1.8-4      2019-04-21 [1] CRAN (R 4.0.0)
   [...]

 [...]
-----------------------------------------------------------------------------------------------------------------------

Packages rstan and StanHeaders are from https://mc-stan.org/r-packages/.

Reproduce the issue by creating schools.stan, launching shinystan with the supplied R code, and opening the ESTIMATE page. Investigate the parameter-selection and regex-search inputs after selecting mu and searching for theta; done means both inputs remain usable and the plot no longer flickers.