Fix Vihko unit fields mishandle typed input and block cursor movement in the trip form

[mikkohei13]

Steps to reproduce

• Open Vihko trip form with a desktop browser. Tested with Firefox on Mac.
• Add an unit

Bug 1

• Add a second unit
• Open the first unit by clicking it
• Quickly after opening it, write "foo" to count field
• Expected: "foo" remains
• Actual: first character disappears, converts to "oo"

Bug 2

• On count or notes field, write something
• Press arrow-left to move cursor
• Expected: cursor moves
• Actual: no effect, cursor remains where it is

Bug 3

• On count or notes field, write "+?-_"
• Expected: those characters appear on the field
• Actual: nothing appeas on the field

Notes

2 and 3 seem to be triggersed by an unknown factor and appear together. If I save the document and open it again, both problems usually disappear.