ISSUEWhen using a Convert Value action in a workflow, commas will be stripped from values where the comma is used to separate numbers in a string. For example "10, 11, 12" becomes "101112".
RESOLUTIONExplicitly define the Culture setting under the Advanced separator. Leaving it blank (default) will strip the comma from the value/string, not substituting it for a proper decimal separator.
For more information about the Culture setting, see Table of Language Culture Names, Codes, and ISO Values Method [C++] in the Microsoft Developer Network.