clicking on tag suggestion inserts abbreviated / truncated tag

### Steps to reproduce
1. launch the h. bookmarklet on a page & sign into your account
2. add an annotation, type something, and assign a new tag, like `testingXYZ`
3. add another annotation, type something and start to type the same tag name => `testingXYZ` will be suggested
4. click on the suggestion

### Expected behaviour
The suggested tag that I clicked on is added.

### Actual behaviour
A truncated tag with just the characters I typed to trigger the drop-down is added.

### Browser/system information
Firefox ESR 52.5.0 (64-Bit) with the bookmarklet (but not in Chrome with the extension!)

### Additional details
Does not occur, when I try tags with which other h. users had tagged their annotations on the same page.