pt-online-schema-change and --set-vars sql_mode not working as expected for modifying column type

Running pt-online-schema-change with --set-vars sql_mode=\'\' to convert a DOUBLE column to DECIMAL(16,4) is not fully working.

Here's a simple test case, first demonstrating how the default SQL modes prevent this alter:

Relaxing sql_mode will allow the truncated conversion of the values:

Now, trying to set sql_mode through the --set-vars option isn't fully working:

I've attached the full output file (/tmp/out2), here's a couple of excerpts from it:

We do see the:

above though. I run pt-osc once again adding --no-drop-new-table:

Inspecting _t1_new it does look to result in the table we want:

Which leaves me clueless as to why the tool is aborting with error 1264 despite the relaxed sql_mode.

I found old https://jira.percona.com/browse/PT-694 but while it also touches --set-vars and sql_mode the problem here seems to be a different one so it doesn't look like a regression.