Yank text to register appends text rather than replacing that register

Describe the bug
When yanking text, for instance, to register a, when I paste that text, it seems to append what I yanked to what was already in that register.

This seems to happen on and off, but more often when using the ctrl-r + register feature in insert mode. (ctrl+r followed by a register inserts that register while in insert mode in actual vim).

A related bug - the . register is supposed to store what you typed last. So using the ctrl-r trick, you should be able to go into insert mode, then press ctrl-r + ., and have it re-type what you previously typed in insert mode. Again, it prepends erroneous characters to the inserted text, usually, the character you used in normal mode to get into insert mode (c, a, I, etc..).

To Reproduce
Steps to reproduce the behaviour:

Yank some text to register a:
ve "ay (text "this")
Yank some more text to register a:
2w ve "ay (text "text")
Paste register a:
"ap or i ctrl-r a
Outputs "thistext" instead of "text" (the last yanked text into that register)

Expected behaviour
yanking to a register should replace that register. pasting from the . register should work as expected.

Environment (please complete the following information):

• Extension (VsCodeVim) version: Latest
• VSCode version: Latest
• OS: Macos Catalina

Start by reproducing the register behavior with the listed normal-mode yanks, "ap, and Ctrl-R in insert mode, including the . register case. Trace the register handling for yanking, pasting, and insert-mode Ctrl-R, then verify that each yank replaces the register and that . retypes only the previous insert-mode text.