ID 266707 - Stepping through field values with arrow keys or scroll wheel affects non-numeric fields

Problem summary
From the Katana 2.5v5 release notes:

TP 82009 / BZ 39886 - Numeric parameter values can now be stepped through using the keyboard arrow keys. Field values can be incremented or decremented by hundreds, tens, tenths hundredths, and so on. The magnitude of change depends on the initial position of the text cursor. For example to increment the initial value of 20.51 by ones, the cursor should be inserted before the 0. This replicates Nuke's behavior.

This behaviour is also applied to string values, even when there is no digit of a numeric value. When there is a string value in the value field, using the arrow keys or scrolling causes the field value to be appended with “(-)#”, so ‘/tmp/test.exr’ becomes ‘/tmp/test.exr1’ etc.
If the field is empty, the value is changed to “(-)#”, so the value will be 1 or -1 up- or downwards depending on the scroll direction. This does not happen in Nuke with fields that have a string value.

Customer reported version
Katana 2.5v5
Customer reported platform
CentOS 7

Steps to reproduce

1. Create a Render node in the node graph

2. Click on the passName field (keep the mouse within the widget)

3. Scroll mouse wheel up or down or hit the up or down arrow key.

4. Result: The passName gets changed to ‘Render1’ or ‘Render-1’ etc. (depending on scroll direction)

Reproduced by support
Katana 2.5v5 Windows 7/RHEL 6.4

Expected behaviour
The scrubbing behaviour should only affect fields with a numeric value, or string values that have a numeric character in them.

Actual behaviour
When there is no numeric digit in the field, one gets appended.