Why can't PDEtools/Solve handle system that solve can?

Hello, I have a simple system that I'm attempting to solve:

eq:={r*cos(c) = a, r*sin(c) = 0}:

If I pass this system to solve(eq, {r,c}), it correctly returns the results {c = 0, r = a}, {c = Pi, r = -a}. However, PDEtools:-Solve(eq, {r,c}) does not find a solution. Even adding the option 'solver'='solve' doesn't help.

According to its help page, PDEtools/Solve is a unified command for solving algebraic or differential equations, so I would expect it to easily handle this system. Is there an additional option I should be passing PDEtools/Solve to make it work like solve in this case?

Thanks!