Drawing upload modal gets very laggy if you have multiple drawings

[carmenfan]

The revision code input box gets really slow when:

• you upload multiple files
• drawing container is filled in

Notice on the screenshot how the revision code input box was still relatively repsonsive, but once i've filled in the other fields it gets quite laggy:

Steps to reproduce

• try to upload many drawings
• fill in drawing destinatino and status code
• try to type in a revision code

Current behaviour

Input box is very laggy - input is coming up much slower than when the characters were typed

Expected behaviour

Should be responsive.