The phenomenon typically occurs when the fountain pen has not been used for a longer time and ink has dried; residues are not completely removed when moving the piston and reach, with the rinsing water, the mechanism. Since the mechanism is today made of plastic, no damage is mostly to be feared. Because of the high value of the Hemingway, the writing instrument should be entrusted to Montblanc service; a complete cleaning with disassembly and replacement of small parts costs up to about €49. In contrast to private repairers, Montblanc can in case of damage provide a replacement.
Related pages on fountainpen.de:
• Montblanc Writers Edition Hemingway (1992): fountainpen.de/writer-hemingway-en.htm