While promoting permissive approaches like this with other organizations I've encountered employers which seem to have a some confusion about the purposes of different parts of their agreement. E.g. an IP agreement is essentially unrelated to making sure an employee is doing their job-- so a "I don't want them spending a lot of time on that" isn't a valid reason to impinge their rights, after all they would be perfectly able to slack off by staring blankly at the coffee pot regardless of what your IP agreement says.
An IP agreement should be about having a clear boundary on company property, it's not a replacement for effective management. Unless you're an operating system company (which to some extent google is, but very few of the innumerable companies that copy google's practices are), trivial fixes to widely used open source software are not good candidates for company property and are not at all candidates for it if developed on the employee's own time.